Sulphur dioxide is a gas formed by oxidation of materials containing sulphur, such as coal, oil, natural gas, industrial and domestic waste and peat. Sulphur dioxide can also be produced as a residual product in chemical processes, for instance in metallurgical processes. It is usually not allowed to emit large quantities of sulphur dioxide into the atmosphere, and therefore some kind of cleaning is necessary. One example is flue gas cleaning in power plants and other combustion plants. The flue gas generated in combustion in such plants is usually cleaned by, inter alia, absorption of sulphur dioxide in an absorption liquid. The absorption liquid may contain, for instance, water and one or more of the substances lime, limestone, dolomite, sodium hydroxide solution and similar substances, which are suitable for absorption of sulphur dioxide.
WO 03/004137 discloses a method and a device for removing sulphur dioxide from a gas. In the method, the flue gas is passed upwards through an apertured plate with a flowing layer of an absorption liquid provided thereon. The absorption liquid that has flown along the apertured plate is collected and made to flow downwards to a container. The flue gas which is to be cleaned first passes through a contact zone, in which it is contacted with the absorption liquid flowing downwards from the apertured plate, and is then passed upwards through the apertured plate. In this manner, it is achieved that the flue gas is saturated with water vapour before it reaches the underside of the apertured plate. However, it has been found that the method according to WO 03/004137 causes an unnecessarily high pressure drop in the contact zone.